Pi [or symbolically π] is possibly one of the most-recognised mathematical constants in the world — besides the "c" in Albert Einstein's most famous equation E=mc^{2} — and there is a day in the year when it is accorded the honour it truly deserves. That day is March 14, and it is marked all around the world in a lot of ways, but mostly by eating pies.

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**What is pi? What is its value?**

Pi is very often described as the ratio of a circle's circumference [the length of the curved line that forms the circle] and the diameter [any straight line from one point on the circumference of the circle to another that passes through its centre]. The formula that connects them is C = 2πR, where C is the circumference and R is the radius [the straight line between the centre of a circle to its circumference, which is exactly half of the diameter].

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However, despite using pi in many mathematical formulae, we have not been able to calculate its exact value. Mathematically, it is called an irrational number, because its digits after the decimal do not have an end, and neither is a series of them repeated anywhere. It has been calculated to 1 trillion digits after the decimal, but for calculation purposes, it is often curtailed at 3.14, or sometimes the fraction 22/7 is used.

**When is Pi Day?**

Because pi is often shortened to 3.14 and the number resembles the date format of March 14, that is when Pi Day is celebrated across the world. Of course, the United States has its own celebration, and has branded the day "National Pi Day."

Elsewhere in the world, it is a geeky, nerdy day where scientists and engineers come together to celebrate the number that is pi, and venerate its uses in theoretical and practical branches of science.

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